The invention relates to a device for determining the conductance of laundry, a dryer and a method for preventing depositing on electrodes for conductance measuring.
In modern dryers, in particular in domestic dryers, the wash moisture in the laundry is measured for controlling the dryer, in particular for achieving desired residual moisture in the laundry. This measuring is preferably carried out according to the principle of conductance measuring.
As a rule two electrodes are applied to the laundry for this purpose, whereby one of the electrodes can represent for example the laundry drum and the second electrode can be a carrier installed against and insulated from the drum. Voltage is applied to the two electrodes via a resistor, and the result is a current through the laundry. The laundry voltage falling on the laundry is measured on the electrodes and from this determines the conductance, which is proportional to the moisture content in the laundry.
It was established in particular with fixed electrodes that a drift in measuring results had been set after repeated use. Tests have proven that this is caused by the development of deposits in the form of layers on the electrodes made by water contents and laundry substances. The transfer resistance occurring from the layers in addition is measured and the result of the wash moisture measuring is thus falsified by these layers, which for example can comprise lime and silicate, during measuring of the wash moisture. This means for example that targeted adjusting of residual moisture in the laundry is no longer guaranteed. On completion of the drying program the final residual moisture of the laundry is rather shifted in the direction of moister laundry. To remove the layers it was suggested to clean the electrode surfaces with acidic cleaning fluids so as to restore the functionality of the wash moisture measuring. This is expensive for one and also the electrodes can be difficult to access for the user, depending on the selected installation site.